Sending email multipart/signed (RFC 3156) via Gmail APIs

Question

Try to build a Message in compliance with RFC3156 [0], and send it via Gmail APIs (I'm using the python client implementation).

What I get is: in my Gmail box, the message is correctly sent (I see exactly the message I built before)·

What my receivers get is: a "multipart/mixed" message with the same payload of the message I sent.

It seems, at some point, Gmail changes my Content-Type ... is this true?

As workaround, I'm using a SMTP connection (which acts like I expect, sends the message correctly), but in the future I would like to avoid this step in favor of a pure Gmail APIs application.

Can you please confirm or not this issue?

[0] - Here a test example:

Sending the message:

message_as_str = '''Content-Type: multipart/signed; protocol="application/pgp-signature";\n micalg="pgp-sha512"; boundary="===============0594182808971957567=="\nMIME-Version: 1.0\nDate: Wed, 12 Nov 2014 12:18:02 +0100\nSubject: A test email\nFrom: Leo Iannacone <[email protected]>\nTo: Andrea Colangelo <[email protected]>\n\n--===============0594182808971957567==\nContent-Type: text/plain; charset="utf-8"\r\nMIME-Version: 1.0\r\nContent-Transfer-Encoding: quoted-printable\r\n\r\nHello,\r\n\r\nthis is a signed email (RFC 3156).\r\n\r\nBest,\r\nL.\r\n\r\n-- =\r\n\r\nUbuntu Member - http://launchpad.net/~l3on\r\nHome Page - http://leoiannacone.com\r\nGPG Key Id - 0xD282FC25\r\n\n--===============0594182808971957567==\nContent-Type: application/pgp-signature; name="signature.asc"\nContent-Description: GooPG digital signature\n\n-----BEGIN PGP SIGNATURE-----\nVersion: GnuPG v1\n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\nuC+56ZJxbKlu73UPsTYh\n=gQKI\n-----END PGP SIGNATURE-----\n\n--===============0594182808971957567==--'''

raw = base64.urlsafe_b64encode(message_as_str)
gmail_service.users().messages().send(userId='me', body={'raw':raw}).execute()

What I have in my sentbox is:

Received: from 333313917298-rr7th7jvf4alej59jkv5bbs2fl8sc0j9.apps.googleusercontent.com
    named unknown
    by gmailapi.google.com
    with HTTPREST;
    Wed, 12 Nov 2014 03:23:50 -0800
Content-Type: multipart/signed; protocol="application/pgp-signature";
 micalg="pgp-sha512"; boundary="===============0594182808971957567=="
MIME-Version: 1.0
Date: Wed, 12 Nov 2014 03:23:50 -0800
Subject: A test email
From: Leo Iannacone <[email protected]>
To: Andrea Colangelo <[email protected]>
Message-Id: <CACzqv1fvmbg2Er0Fi-poFSfEDaCLXxW-WGQr8dwHma6t9NjBzA@mail.gmail.com>

--===============0594182808971957567==
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable

Hello,

this is a signed email (RFC 3156).

Best,
L.

-- =

Ubuntu Member - http://launchpad.net/~l3on
Home Page - http://leoiannacone.com
GPG Key Id - 0xD282FC25

--===============0594182808971957567==
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: GooPG digital signature

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=gQKI
-----END PGP SIGNATURE-----

--===============0594182808971957567==--

What my receiver get is exaclty:

Delivered-To: [email protected]
Received: by 10.70.104.40 with SMTP id gb8csp207478pdb;
        Wed, 12 Nov 2014 03:23:54 -0800 (PST)
X-Received: by 10.194.94.132 with SMTP id dc4mr64238431wjb.56.1415791433615;
        Wed, 12 Nov 2014 03:23:53 -0800 (PST)
Return-Path: <[email protected]>
Received: from fiordland.canonical.com (fiordland.canonical.com. [91.189.94.145])
        by mx.google.com with ESMTP id 16si39684910wjr.38.2014.11.12.03.23.53
        for <[email protected]>;
        Wed, 12 Nov 2014 03:23:53 -0800 (PST)
Received-SPF: softfail (google.com: domain of transitioning [email protected] does not designate 91.189.94.145 as permitted sender) client-ip=91.189.94.145;
Authentication-Results: mx.google.com;
       spf=softfail (google.com: domain of transitioning [email protected] does not designate 91.189.94.145 as permitted sender) [email protected]
Received: from mail-ig0-f170.google.com (mail-ig0-f170.google.com [209.85.213.170])
    by fiordland.canonical.com (Postfix) with ESMTPS id ABACCA183B1
    for <[email protected]>; Wed, 12 Nov 2014 11:23:52 +0000 (UTC)
Received: by mail-ig0-f170.google.com with SMTP id a13so1193944igq.5
        for <[email protected]>; Wed, 12 Nov 2014 03:23:51 -0800 (PST)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=1e100.net; s=20130820;
        h=mime-version:from:date:message-id:subject:to:content-type;
        bh=W/iDzPadzt4k3bMV8jLK7/5iZLI23kjqCuGNPJ0hdzY=;
        b=MFCFT42IlWfQzbXCCG5slCE4vzpsZg2WQpkmwFa7L46b61Yd/zQ522GgPA1rRhsSrP
         pHhuhPUfCy6HjZRIFf8GqgtTPhinLiuli+ClOz6Oe9rvjH2JK5ILxf0+17woL1n48QAW
         xHnJfo8A/qhBvN42AfdSNVhvcQqQObZ25wBe08zwDJeEWT2XRRiDXcWdWagyqisTronc
         kj3CwRj5AOBThEpzA+wPC0Aalofqqu+YMIMuchBoTsfh437BxkHJLg+il6kDobJXVtXB
         9OPc8o2JqtWwnzHEkC6QKFG54ddoPwvuyq6S325zuDfuKoVrLGeC/kzWRQP+SudBTw0J
         RWBA==
X-Received: by 10.107.135.146 with SMTP id r18mr1699637ioi.62.1415791431765;
 Wed, 12 Nov 2014 03:23:51 -0800 (PST)
Received: from 333313917298-rr7th7jvf4alej59jkv5bbs2fl8sc0j9.apps.googleusercontent.com
 named unknown by gmailapi.google.com with HTTPREST; Wed, 12 Nov 2014 03:23:50 -0800
MIME-Version: 1.0
From: Leo Iannacone <[email protected]>
Date: Wed, 12 Nov 2014 03:23:50 -0800
Message-ID: <CACzqv1fvmbg2Er0Fi-poFSfEDaCLXxW-WGQr8dwHma6t9NjBzA@mail.gmail.com>
Subject: A test email
To: Andrea Colangelo <[email protected]>
Content-Type: multipart/mixed; boundary=001a113f96625df1a80507a7a1d8

--001a113f96625df1a80507a7a1d8
Content-Type: text/plain; charset=ISO-8859-1

Hello,

this is a signed email (RFC 3156).

Best,
L.

-- 
Ubuntu Member - http://launchpad.net/~l3on
Home Page - http://leoiannacone.com
GPG Key Id - 0xD282FC25

--001a113f96625df1a80507a7a1d8
Content-Type: application/pgp-signature; name="signature.asc"
Content-Disposition: attachment; filename="signature.asc"
Content-Transfer-Encoding: base64
X-Attachment-Id: bc758a9561fcd7dc_0.1
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--001a113f96625df1a80507a7a1d8--

As you can see... The content type is different from what I have in my sent mails, and what my receive get in his inbox.

Answer 1

From my testing this appears to be an issue with the Gmail API. It's unclear if the API plans to support this use case, but I've raised the issue with the engineering team.